The objectives of this proposal are: a) to obtain a clearer understanding of the basic metabolic defects in the various clinical forms of acid alpha-glucosidase deficiency; b) to evaluate the ability of purified human enzyme from various sources to correct the metabolic defect in cultured muscle cells (the primarily affected type of cells) derived from patients with acid alpha-glucosidase deficiency: d) to study the catalytic, immunologic, and physichemical properties of an electrophoretic variant of the acid isozyme of alpha-glucosidase which appears to be deficient towards the natural substrate glycogen; and e) to measure the enzyme activity in cells from homozygotes and heterozygotes for the variant isozyme of acid alpha-gulcosidase. Acid alpha-glucosidase will be purified using several purification steps, including affinity chromatography, from placentae and from both normal and deficient cultured skin fibroblasts. Physicochemical (electrophoretic mobility molecular weight, sedimentation coefficient, susceptibility to thermal denaturation), immunologic (prescence or absence of cross-reacting material (CRM), amount and immunologic (presence or absence of cross-reacting material (CRM), amount and immunologic identity of CRM in the various clinical forms of the disease) and catalytic properties (Km, Vmax, pH optimum, substrate specificity, inhibition characteristics) will be studied. The rate of synthesis and degradation of acid alpha-glucosidase in cultured skin fibroblasts from normal and deficient individuals will be measured. Acid alpha-glucosidase purified to homogeneity will be added to the culture medium of deficient cultured muscle cells. The ability of the exogenous enzyme to correct the metabolic defect in the cultured cells will be determined by microscopy and measurement of its effect on glycogen accumulation. Acid alpha-glucosidase activity will be measured in placentae, peripheral leukocytes, and cultured skin fibroblasts from individuals homozygous and heterozygous for the variant isozyme of acid alpha-glucosidase using three different substrates, including glycogen.